1. Field of the Invention
The present invention relates to a liquid ejection substrate and a liquid ejection head using the liquid ejection substrate. More specifically, the present invention relates to an inkjet printhead substrate and an inkjet print head using the inkjet printhead substrate.
2. Description of the Related Art
Usually, a plurality of heating elements (hereinafter referred to as heaters) of a printhead complying with a liquid ejection system, and a plurality of drive circuits used for the heating elements, and a plurality of conducive traces used for the heating elements are provided on the same substrate by using a semiconductor processing technology, as disclosed in U.S. Pat. No. 7,216,960.
There has been the demand for downsizing inkjet print heads configured to eject a liquid such as ink, as the resolution and/or the speed of the inkjet print head has been increased. Further, an increase in the density of arrangement of heaters and/or drive circuits, an increase in the number of rows, the increase being made to increase the number of ink colors, and an increase in the number of heaters have been demanded. However, if the density, the row number, and the length of the printhead substrate are simply increased, the circuit scale is naturally increased so that the substrate and the printhead are increased in size. Therefore, a conversion circuit of a heating-resistance-element drive power has been proposed as disclosed in U.S. Pat. No. 7,267,429, so as to decrease the circuit scale.
Since the inkjet print head should be used with stability under various circumstances, the temperatures of the printhead substrate and ink should be controlled so as to ensure the ink ejection ability. Therefore, it is widely known that a subheater (hereinafter referred to as a heating portion) is provided in the substrate, and when the temperature of the substrate and/or the ink is low, the temperature of the substrate is adjusted.
FIG. 13 shows an ordinary inkjet printhead substrate (hereinafter referred to as a printhead substrate). Heating resistance elements and drive circuits 1300 are provided by using a semiconductor processing technology. The above-described substrate includes a first conductive layer provided as a lower conductive layer and a second conductive layer provided as an upper conductive layer, which constitutes a multilayer configuration. The substrate is provided with an input-and-output pad 1301 provided as a point of electrical contact with outside and two adjacent ink supplying ports 1302 that are used to supply ink from the back face. Hereinafter, an area between the two adjacent ink supplying ports 1302 will be referred to as an area between colors.
Each of drive circuits 1303 which select the heating resistance elements includes, for example, a shift register circuit, a latch circuit, a decoder circuit, and so forth. Further, a heating resistance element row 1304 is connected to a driver portion 1305 used to drive the heating resistance element row 1304 and a logic circuit 1306 that selects an arbitrary driver portion and that supplies a voltage to the gate of the driver 1305 corresponding to the selected driver. Further, a plurality of logic signal line areas 1307 is provided to transmit a signal to the driver circuit 1303 and/or the logic circuit 1306.
A signal generated to select a heating resistor for driving is transmitted to the logic signal line area 1307. Eventually, the logic signal line area 1307 is used to supply a voltage to the gate of the driver portion 1305 and drive the heating resistor.
In recent years, the sizes of chips have been downsized and the densities of the chips have been increased. Therefore, a subheater should be provided without increasing the area of an ordinary head substrate such as the substrate shown in FIG. 13. The subheater is driven asynchronously with driving of a heating resistance element at a relatively high temperature so as to obtain a power consumption used to achieve heat insulation. If the subheater driven in the above-described circumstances is provided in an area defined near the logic signal line area 1307, a noise occurring when the subheater is controlled may be propagated to a low-voltage logic signal line 1307 so that a printing operation may be performed incorrectly.
An influence of the above-described noise is a phenomenon usually referred to as a crosstalk noise, which means that fluctuations in a signal line are moved to a different signal line. The above-described noise is affected by a capacitance between traces. Therefore, the noise is increased with increasing capacitance. The relationship between the capacitance, the cross sectional area of traces, two traces, and a distance between the traces is expressed by the equation:C=εS/d, 
where the sign C denotes a capacitance, the sign ε denotes a permittivity, the sign S denotes a cross sectional area, and the sign d denotes a distance. Therefore, a distance should be put between the traces.